Looks like someone else had the same question re. the rate limit
I haven't used it personally, but there's a package, ratelimitr, that will let you set a rate limit on any R function:
From the README:
library(ratelimitr)
f <- function() NULL
# create a version of f that can only be called 10 times per second
f_lim <- limit_rate(f, rate(n = 10, period = 1))
# time without limiting
system.time(replicate(11, f()))
#> user system elapsed
#> 0 0 0
# time with limiting
system.time(replicate(11, f_lim()))
#> user system elapsed
#> 0.00 0.00 1.05